So everyone's heard of Gravity. The thing that brings you down to earth and keeps you there. Of course almost nobody knows what it actually is. Some people know about Newton and the Apple and some people even know about Einstein's General Theory of Relativity. But how do they paint the image of Gravity?
So lets start from Newton. In 1687, he published the Principia ( Philosophiæ Naturalis Principia Mathematica) in which he includes this definition for the law of universal gravitation: Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force experienced is calculated as,
F=G{frac {m_{1}m_{2}}{r^{2}}}
Where F is force, G is the gravitational constant, m is the mass (with the small 1 and 2 at the bottom being the mass of first object and second object) and r being the distance between the two objects. F is usually calculated with Newtons (N), m with kilograms (kg) and r with metres (m). The constant G, calculated about after a hundred so years, is 6.674×10−11 N m2 kg−2.
The line in his book Principia (which was written in Latin) basically means that anything with mass will attract any other thing with mass at the force calculated by that formula. This force is always attractive, meaning to say that the objects are attracted to one another. At this point you might be asking yourself, what about us and the Earth? Well Newton's three laws of motion shows us that something with lesser mass accelerates faster than something with more mass, thus we accelerate at a much faster rate than the Earth.
Now some time later someone named Albert Einstein formed the Special Theory of Relativity and in it he did not add in the factor that gravity plays. Thus he formed the General Theory of Relativity in which gravity is now a factor. Theory of Relativity basically states that first; Everything observed or measured is relative to the velocity of the observer or measurer, which means space and time can dilate, second; Space and Time should be considered together and are in relation to each other and thirdly; the speed of light is the same for all observers.
To understand what the first point means, let's say Peter and Mary are at a train platform. Peter is going off and Mary is there to send him off. Now as the train starts moving, Peter starts bouncing a basketball up and down. Mary watches as the train moves off and now you would realise that even though they are observing the same thing, Peter's observation of how the ball is moving will be different from Mary's. Peter would see the ball going directly down and up while Mary will see the ball going down at an angle before bouncing up at the same angle to Peter's hand. Here we say the ball is bouncing at an angle RELATIVE to Mary as it will only seem that way to her but not to Peter.
Now that we got that out of the way, we can continue on gravity. Einstein realised that Newton's law of universal gravitation only works in some situations, like low gravity situations. In order to accommodate gravity into his Theory of Relativity, he had to form a new model for gravity. Upon forming his theory, he realised that gravity is caused by mass distorting Space-time, causing curvatures in Space-time.
To understand this, let's pretend that Space-time is a trampoline, Now imagine that Earth is a bowling ball. We place the bowling ball on the trampoline and this causes an depression in the trampoline, causing the trampoline to curve towards the bowling ball. Newton's view of gravity (as far as I'm aware) did not explain the attraction between objects. However, Einstein's one does. It explains that the attraction is caused by the curvature of Space-time. To picture this, imagine rolling a marble close to the bowling ball. The curvature of the trampoline around it will make the ball roll in, similar to how gravity would attract something with mass to another thing with mass.
Using this, Einstein realised several things. One of the things is that gravity does not only affect things with mass. Take light for example. Einstein's famous E= mc squared says that anything with energy will definitely have mass. But for light to travel at its speed, it has to possess no mass. Light (consisting of photons) is however affected by gravity. Upon nearing a strong enough force of gravity, light will actually bend, sometimes even getting sucked into the source of the gravitational pull (example a black hole).
Gravity also affects time. The stronger the force of gravity at an area, the slower time passes for that particular area. This is due to the fact that, if you remember, space and time should be considered together and in relation to each other. When the body of mass creates curvature in space-time, time is also affected. This particular effect is called Gravitational Time Dilation.
But why does this all matter? Well, for one without considering all this factors than your GPS will lose more than 10km per day. This is because satellites taking your position are orbiting Earth at high speeds. While travelling at high speeds, the mass of the particular body increases, which can be shown using E=mc squared. As you go faster, the energy (E) increases and as c squared is a constant, as E increases m (mass) increases as well. Since the curvature around a body relies on its mass, the higher the mass the more gravitational force you feel and therefore time passes slower. Without formulas derived from Einstein's Theory of Relativity, the corrections needed to guide you to the nearest 7-11 wouldn't be possible.
So lets start from Newton. In 1687, he published the Principia ( Philosophiæ Naturalis Principia Mathematica) in which he includes this definition for the law of universal gravitation: Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force experienced is calculated as,
Where F is force, G is the gravitational constant, m is the mass (with the small 1 and 2 at the bottom being the mass of first object and second object) and r being the distance between the two objects. F is usually calculated with Newtons (N), m with kilograms (kg) and r with metres (m). The constant G, calculated about after a hundred so years, is 6.674×10−11 N m2 kg−2.
The line in his book Principia (which was written in Latin) basically means that anything with mass will attract any other thing with mass at the force calculated by that formula. This force is always attractive, meaning to say that the objects are attracted to one another. At this point you might be asking yourself, what about us and the Earth? Well Newton's three laws of motion shows us that something with lesser mass accelerates faster than something with more mass, thus we accelerate at a much faster rate than the Earth.
Now some time later someone named Albert Einstein formed the Special Theory of Relativity and in it he did not add in the factor that gravity plays. Thus he formed the General Theory of Relativity in which gravity is now a factor. Theory of Relativity basically states that first; Everything observed or measured is relative to the velocity of the observer or measurer, which means space and time can dilate, second; Space and Time should be considered together and are in relation to each other and thirdly; the speed of light is the same for all observers.
To understand what the first point means, let's say Peter and Mary are at a train platform. Peter is going off and Mary is there to send him off. Now as the train starts moving, Peter starts bouncing a basketball up and down. Mary watches as the train moves off and now you would realise that even though they are observing the same thing, Peter's observation of how the ball is moving will be different from Mary's. Peter would see the ball going directly down and up while Mary will see the ball going down at an angle before bouncing up at the same angle to Peter's hand. Here we say the ball is bouncing at an angle RELATIVE to Mary as it will only seem that way to her but not to Peter.
Now that we got that out of the way, we can continue on gravity. Einstein realised that Newton's law of universal gravitation only works in some situations, like low gravity situations. In order to accommodate gravity into his Theory of Relativity, he had to form a new model for gravity. Upon forming his theory, he realised that gravity is caused by mass distorting Space-time, causing curvatures in Space-time.
To understand this, let's pretend that Space-time is a trampoline, Now imagine that Earth is a bowling ball. We place the bowling ball on the trampoline and this causes an depression in the trampoline, causing the trampoline to curve towards the bowling ball. Newton's view of gravity (as far as I'm aware) did not explain the attraction between objects. However, Einstein's one does. It explains that the attraction is caused by the curvature of Space-time. To picture this, imagine rolling a marble close to the bowling ball. The curvature of the trampoline around it will make the ball roll in, similar to how gravity would attract something with mass to another thing with mass.
Using this, Einstein realised several things. One of the things is that gravity does not only affect things with mass. Take light for example. Einstein's famous E= mc squared says that anything with energy will definitely have mass. But for light to travel at its speed, it has to possess no mass. Light (consisting of photons) is however affected by gravity. Upon nearing a strong enough force of gravity, light will actually bend, sometimes even getting sucked into the source of the gravitational pull (example a black hole).
Gravity also affects time. The stronger the force of gravity at an area, the slower time passes for that particular area. This is due to the fact that, if you remember, space and time should be considered together and in relation to each other. When the body of mass creates curvature in space-time, time is also affected. This particular effect is called Gravitational Time Dilation.
But why does this all matter? Well, for one without considering all this factors than your GPS will lose more than 10km per day. This is because satellites taking your position are orbiting Earth at high speeds. While travelling at high speeds, the mass of the particular body increases, which can be shown using E=mc squared. As you go faster, the energy (E) increases and as c squared is a constant, as E increases m (mass) increases as well. Since the curvature around a body relies on its mass, the higher the mass the more gravitational force you feel and therefore time passes slower. Without formulas derived from Einstein's Theory of Relativity, the corrections needed to guide you to the nearest 7-11 wouldn't be possible.